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2.96.89.113: /* Functionality */ Fixed math-enviro for consistency.

2014-10-05T22:24:40Z

Functionality: Fixed math-enviro for consistency.

← Older revision		Revision as of 00:24, 6 October 2014
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	~~{{Acids and bases}}~~		Hi there, I am Sophia. My spouse doesn't like it the way I do but what I truly like doing is caving but I don't have the time recently. For many years she's been living in Kentucky but her husband desires them to move. Office supervising is where my main earnings comes from but I've always needed my personal company.<br><br>my blog: [http://kard.dk/?p=24252 online psychic]
	~~The '''Hammett acidity function''' (H<sub>0</sub>) is a measure of acidity that is used for very concentrated solutions of strong [[acid]]s~~, ~~including [[superacid]]s~~. ~~It was proposed by~~ the ~~physical organic chemist [[Louis Plack Hammett]]<ref>L.P. Hammett and A.J. Deyrup (1932) J. Am. Chem. Soc. 54, 2721</ref><ref>L.P. Hammett (1940). Physical Organic Chemistry. (McGraw-Hill)</ref> and~~ is ~~the best-known [[acidity function]] used to extend the measure of [[Brønsted-Lowry]] acidity beyond the dilute aqueous solutions for which the [[pH]] scale is useful.~~

	In highly concentrated solutions, simple approximations such as the [[Henderson-Hasselbalch equation]] are no longer valid due to the variations of the [[activity coefficient]]s. The Hammett acidity function is used in fields such as [[physical organic chemistry]] for the study of acid-catalyzed reactions, because some of these reactions use acids in very high concentrations, or even neat (pure).<ref name=poc>Gerrylynn K. Roberts, Colin Archibald Russell. '~~'Chemical History: Reviews of~~ the ~~Recent Literature''~~. ~~Royal Society of Chemistry,~~ '~~''2005'''. ISBN 0-85404-464-7.</ref>~~

	~~==Definition==~~
	The Hammett acidity function, H<sub>0</sub>, can replace the [[pH]] in concentrated solutions. It is defined using an equation<ref name=Jolly>William L. Jolly, "Modern Inorganic Chemistry" (McGraw-Hill 1984), p.202-3</ref><ref>F.A. Cotton and G. Wilkinson, "Advanced Inorganic Chemistry" (5th edition, Wiley-Interscience 1988), p.107-9</ref><ref>G.L. Miessler and D.A. Tarr, "Inorganic Chemistry" (2nd edition, Prentice-Hall 1999), p.170-1</ref> analogous to the Henderson-Hasselbalch equation:

	~~:<math>H_{0} = \mbox{p}K_{BH^+} + \log \frac{[B]}{[BH^+]}</math>~~

	where log(x) is the [[common logarithm]] of x, and p''K''<sub>BH<sup>+</sup></sub> is −log(K) for the dissociation of BH<sup>+</sup>, which is the [[conjugate acid]] of a very weak base B, with a very negative p''K''<sub>BH<sup>+</sup></sub>. In this way, it is rather as if the pH scale has been ~~extended to very negative values. Hammett originally used a series of [[aniline]]s with [[electron-withdrawing group]]s for the bases.<ref name=poc/>~~

	~~Hammett also pointed out the equivalent form~~

	~~:<math>H_{0} = -\log \left ( a_{H^+} \frac{\gamma_B}{\gamma_{BH^+}} \right )</math>~~

	where ''a'' is the activity, and the γ are thermodynamic [[activity coefficients]]. In dilute aqueous solution (pH 0-14) the predominant acid species is H<sub>3</sub>O<sup>+</sup> and the activity coefficients are close to unity, so H<sub>0</sub> is approximately equal to the pH. However beyond this pH range, the effective hydrogen-ion activity changes much more rapidly than the concentration.<ref name=Jolly/> This is often due to changes in ~~the nature of the acid species; for example in concentrated [[sulfuric acid]], the predominant acid species ("H+") is not H<sub>3</sub>O<sup>+</sup>~~ but rather H<sub>3</sub>SO<sub>4</sub><sup>+</sup> which is a much stronger acid. The value H<sub>0</sub> = -12 for pure sulfuric acid must not be interpreted as pH = -12 (which would imply an impossibly high H<sub>3</sub>O<sup>+</sup> concentration of 10<sup>+12</sup> mol/L in ideal solution). Instead it means that the acid species present (H<sub>3</sub>SO<sub>4</sub><sup>+</sup>) has a protonating ability equivalent to H<sub>3</sub>O<sup>+</sup> at a fictitious (ideal) concentration of 10<sup>12</sup> mol/L, as measured by its ability to ~~protonate weak bases~~.

	~~Although the Hammett acidity function~~ is ~~the best known [[acidity function]], other acidity functions have been developed by authors such as Arnett, Cox, Katrizky, Yates, and Stevens.<ref name=poc/>~~

	~~==Typical values==~~
	On this scale, pure [[sulfuric acid\|H<sub>2</sub>SO<sub>4</sub>]] (18.4 [[Concentration#Molarity\|M]]) has a ''H''<sub>0</sub> value of −12, and [[pyrosulfuric acid]] has ''H''<sub>0</sub> ~ −15.<ref>[http://www.scienceinafrica.co.za/2002/august/ph.htm What do you mean pH = -1? Super Acids<!-- Bot generated title -->]</ref> Take note that the Hammett acidity function clearly avoids water in its equation. It is a generalization of the pH scale—in a dilute aqueous solution (where B is H<sub>2</sub>O), pH is very nearly equal to ''H''<sub>0</sub>. By using a solvent-independent quantitative measure of acidity, the implications of the [[leveling effect]] are eliminated, and it becomes possible to directly compare the acidities of different substances (e.g. using p''K''<sub>a</sub>, HF is weaker than HCl or H<sub>2</sub>SO<sub>4</sub> in water but ~~stronger than HCl in glacial acetic acid; and pure HF is "stronger" than H<sub>2</sub>SO<sub>4</sub> because the~~ '~~'H''<sub>0</sub> of pure HF is higher than that of pure H<sub>2</sub>SO<sub>4</sub>~~.<~~ref~~>~~"The Hammett Acidity Function H~~<~~sub~~>~~0</sub> for Hydrofluoric Acid Solutions." Herbert H. Hyman, Martin Kilpatrick, Joseph J. Katz, J. Am. Chem. Soc., 1957, 79 (14), pp 3668–3671 {{doi\|10.1021/ja01571a016}} http~~://pubs.acs.org/doi/abs/10.1021/ja01571a016</ref><ref>Liang, Jack Joan-Nan, "The Hammett Acidity Function for Hydrofluoric Acid and some related Superacid Systems" (1976). Open Access Dissertations and Theses. Paper 3850. http://~~digitalcommons.mcmaster~~.ca/~~opendissertations/3850</ref>)~~

	~~H<sub>0</sub> for some concentrated acids:{{Citation needed\|date~~=~~November 2007}}~~
	* [[Fluoroantimonic acid]] (1990): −31.3
	* [[Magic acid]] (1974): −19.2
	* [[Carborane superacid]] (1969): −18.0
	* [[Fluorosulfuric acid]] (1944): −15.1
	* [[Triflic acid]] (1940): −14.1
	* [[Chlorosulfuric acid\|Chlorosulfuric Acid]] (1978): -12.78 <ref>The Chemistry of Nonaqueous Solvents VB: Acid and Aprotic Solvents Ed J.J. Lagowski, pp139, Academic Press, London, 1978</ref>
	* [[Sulfuric acid\|Sulfuric acid:]] −12.0

	For mixtures (e.g., partly diluted acids in water), the acidity function depends on the composition of the mixture and has to be determined empirically. Graphs of H<sub>0</sub> vs [[mole fraction]] can be found in the literature for many acids.<ref name=poc/>

	~~==References==~~
	~~<references />~~

	~~{{Chemical equilibria}}~~

	~~[[Category:Acid-base chemistry]]~~
	~~[[Category:Physical organic chemistry]]~~
	~~[[Category:Superacids\|*]~~]

en>ChrisGualtieri: General Fixes + CheckWiki 75 using AWB

2013-10-27T22:39:33Z

General Fixes + CheckWiki 75 using AWB

← Older revision		Revision as of 00:39, 28 October 2013
Line 1:		Line 1:
	~~I would like~~ to ~~introduce myself~~ to ~~you~~, ~~I am Andrew~~ and ~~my spouse doesn~~'~~t like~~ it ~~at all~~. ~~For years she~~'~~s been operating as~~ a ~~travel agent~~. ~~To climb~~ is ~~something she would by no means give up~~. ~~Mississippi~~ is ~~where her home~~ is but ~~her husband wants them~~ to ~~move~~.<br><br>~~my webpage: psychic love readings~~ [[http://www.~~prograd~~.~~uff~~.br/~~novo~~/~~facts~~-~~about~~-~~growing~~-~~greater~~-~~organic~~-~~garden www~~.~~prograd~~.~~uff~~.br]]		{{Acids and bases}}
			The '''Hammett acidity function''' (H<sub>0</sub>) is a measure of acidity that is used for very concentrated solutions of strong [[acid]]s, including [[superacid]]s. It was proposed by the physical organic chemist [[Louis Plack Hammett]]<ref>L.P. Hammett and A.J. Deyrup (1932) J. Am. Chem. Soc. 54, 2721</ref><ref>L.P. Hammett (1940). Physical Organic Chemistry. (McGraw-Hill)</ref> and is the best-known [[acidity function]] used to extend the measure of [[Brønsted-Lowry]] acidity beyond the dilute aqueous solutions for which the [[pH]] scale is useful.

			In highly concentrated solutions, simple approximations such as the [[Henderson-Hasselbalch equation]] are no longer valid due to the variations of the [[activity coefficient]]s. The Hammett acidity function is used in fields such as [[physical organic chemistry]] for the study of acid-catalyzed reactions, because some of these reactions use acids in very high concentrations, or even neat (pure).<ref name=poc>Gerrylynn K. Roberts, Colin Archibald Russell. ''Chemical History: Reviews of the Recent Literature''. Royal Society of Chemistry, '''2005'''. ISBN 0-85404-464-7.</ref>

			==Definition==
			The Hammett acidity function, H<sub>0</sub>, can replace the [[pH]] in concentrated solutions. It is defined using an equation<ref name=Jolly>William L. Jolly, "Modern Inorganic Chemistry" (McGraw-Hill 1984), p.202-3</ref><ref>F.A. Cotton and G. Wilkinson, "Advanced Inorganic Chemistry" (5th edition, Wiley-Interscience 1988), p.107-9</ref><ref>G.L. Miessler and D.A. Tarr, "Inorganic Chemistry" (2nd edition, Prentice-Hall 1999), p.170-1</ref> analogous to the Henderson-Hasselbalch equation:

			:<math>H_{0} = \mbox{p}K_{BH^+} + \log \frac{[B]}{[BH^+]}</math>

			where log(x) is the [[common logarithm]] of x, and p''K''<sub>BH<sup>+</sup></sub> is −log(K) for the dissociation of BH<sup>+</sup>, which is the [[conjugate acid]] of a very weak base B, with a very negative p''K''<sub>BH<sup>+</sup></sub>. In this way, it is rather as if the pH scale has been extended to very negative values. Hammett originally used a series of [[aniline]]s with [[electron-withdrawing group]]s for the bases.<ref name=poc/>

			Hammett also pointed out the equivalent form

			:<math>H_{0} = -\log \left ( a_{H^+} \frac{\gamma_B}{\gamma_{BH^+}} \right )</math>

			where ''a'' is the activity, and the γ are thermodynamic [[activity coefficients]]. In dilute aqueous solution (pH 0-14) the predominant acid species is H<sub>3</sub>O<sup>+</sup> and the activity coefficients are close to unity, so H<sub>0</sub> is approximately equal to the pH. However beyond this pH range, the effective hydrogen-ion activity changes much more rapidly than the concentration.<ref name=Jolly/> This is often due to changes in the nature of the acid species; for example in concentrated [[sulfuric acid]], the predominant acid species ("H+") is not H<sub>3</sub>O<sup>+</sup> but rather H<sub>3</sub>SO<sub>4</sub><sup>+</sup> which is a much stronger acid. The value H<sub>0</sub> = -12 for pure sulfuric acid must not be interpreted as pH = -12 (which would imply an impossibly high H<sub>3</sub>O<sup>+</sup> concentration of 10<sup>+12</sup> mol/L in ideal solution). Instead it means that the acid species present (H<sub>3</sub>SO<sub>4</sub><sup>+</sup>) has a protonating ability equivalent to H<sub>3</sub>O<sup>+</sup> at a fictitious (ideal) concentration of 10<sup>12</sup> mol/L, as measured by its ability to protonate weak bases.

			Although the Hammett acidity function is the best known [[acidity function]], other acidity functions have been developed by authors such as Arnett, Cox, Katrizky, Yates, and Stevens.<ref name=poc/>

			==Typical values==
			On this scale, pure [[sulfuric acid\|H<sub>2</sub>SO<sub>4</sub>]] (18.4 [[Concentration#Molarity\|M]]) has a ''H''<sub>0</sub> value of −12, and [[pyrosulfuric acid]] has ''H''<sub>0</sub> ~ −15.<ref>[http://www.scienceinafrica.co.za/2002/august/ph.htm What do you mean pH = -1? Super Acids<!-- Bot generated title -->]</ref> Take note that the Hammett acidity function clearly avoids water in its equation. It is a generalization of the pH scale—in a dilute aqueous solution (where B is H<sub>2</sub>O), pH is very nearly equal to ''H''<sub>0</sub>. By using a solvent-independent quantitative measure of acidity, the implications of the [[leveling effect]] are eliminated, and it becomes possible to directly compare the acidities of different substances (e.g. using p''K''<sub>a</sub>, HF is weaker than HCl or H<sub>2</sub>SO<sub>4</sub> in water but stronger than HCl in glacial acetic acid; and pure HF is "stronger" than H<sub>2</sub>SO<sub>4</sub> because the ''H''<sub>0</sub> of pure HF is higher than that of pure H<sub>2</sub>SO<sub>4</sub>.<ref>"The Hammett Acidity Function H<sub>0</sub> for Hydrofluoric Acid Solutions." Herbert H. Hyman, Martin Kilpatrick, Joseph J. Katz, J. Am. Chem. Soc., 1957, 79 (14), pp 3668–3671 {{doi\|10.1021/ja01571a016}} http://pubs.acs.org/doi/abs/10.1021/ja01571a016</ref><ref>Liang, Jack Joan-Nan, "The Hammett Acidity Function for Hydrofluoric Acid and some related Superacid Systems" (1976). Open Access Dissertations and Theses. Paper 3850. http://digitalcommons.mcmaster.ca/opendissertations/3850</ref>)

			H<sub>0</sub> for some concentrated acids:{{Citation needed\|date=November 2007}}
			* [[Fluoroantimonic acid]] (1990): −31.3
			* [[Magic acid]] (1974): −19.2
			* [[Carborane superacid]] (1969): −18.0
			* [[Fluorosulfuric acid]] (1944): −15.1
			* [[Triflic acid]] (1940): −14.1
			* [[Chlorosulfuric acid\|Chlorosulfuric Acid]] (1978): -12.78 <ref>The Chemistry of Nonaqueous Solvents VB: Acid and Aprotic Solvents Ed J.J. Lagowski, pp139, Academic Press, London, 1978</ref>
			* [[Sulfuric acid\|Sulfuric acid:]] −12.0

			For mixtures (e.g., partly diluted acids in water), the acidity function depends on the composition of the mixture and has to be determined empirically. Graphs of H<sub>0</sub> vs [[mole fraction]] can be found in the literature for many acids.<ref name=poc/>

			==References==
			<references />

			{{Chemical equilibria}}

			[[Category:Acid-base chemistry]]
			[[Category:Physical organic chemistry]]
			[[Category:Superacids\|*]]

87.112.88.127 at 14:30, 25 August 2012

2012-08-25T14:30:19Z

New page

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